tea1099h NXP Semiconductors, tea1099h Datasheet - Page 12

• Manufacturer Part Number: tea1099h
• Description: Speech And Handsfree Ic With Auxiliary Inputs/outputs And Analog Multiplexer
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Handsfree application
As can be seen from Fig.3, a loop is formed via the
sidetone network in the line interface part and the acoustic
coupling between loudspeaker and microphone of the
handsfree part. When this loop gain is greater than 1,
howling occurs. In a full duplex application, this would be
the case. The loop-gain has to be much lower than 1 and
therefore has to be decreased to avoid howling. This is
achieved by the duplex controller. The duplex controller of
the TEA1099H detects which channel has the ‘largest’
signal and then controls the gain of the microphone
amplifier and the loudspeaker amplifier so that the sum of
the gains remains constant.
As a result, the circuit in this handsfree application can be
in three stable modes:
1. Transmit mode (TX mode).
2. Receive mode (RX mode).
3. Idle mode.
1999 Apr 08
handbook, full pagewidth
Speech and handsfree IC with auxiliary
inputs/outputs and analog multiplexer
The gain of the microphone amplifier is at its maximum
and the gain of the loudspeaker amplifier is at its
minimum.
The gain of the loudspeaker amplifier is at its
maximum and the gain of the microphone amplifier is
at its minimum.
The gain of the amplifiers is halfway between their
maximum and minimum value.
telephone
line
sidetone
Fig.6 Handsfree telephone set principles.
HYBRID
12
The difference between the maximum gain and minimum
gain is called the switching range.
H
TXOUT
The TEA1099H has an asymmetrical handsfree
microphone input TXIN with an input resistance of 20 k .
The DC biasing of the input is 0 V. The gain of the input
stage varies according to the mode of the TEA1099H.
In the transmit mode, the gain is at its maximum; in the
receive mode, it is at its minimum and in the Idle mode it is
halfway between maximum and minimum.
Switch-over from one mode to the other is smooth and
click-free. The output TXOUT is biased at two diodes
voltage and has a current capability equal to 20 A (RMS).
In the transmit mode, the overall gain of the microphone
amplifier (from pins TXIN to TXOUT) can be adjusted from
0 up to 31 dB to suit specific application requirements.
The gain is proportional to the value of R
15.2 dB with R
output, the microphone input stage can accommodate
signals up to 18 mV (RMS) at room temperature for 2% of
THD.
ANDSFREE MICROPHONE CHANNEL
CONTROL
DUPLEX
AND
GNDTX (see Fig.7)
GATX
= 30.1 k . Without limitation from the
MGM299
coupling
acoustic
:
PINS
Product specification
TEA1099H
TXIN, GATX,
GATX
and equals